This invention relates to semiconductor devices and, more particularly, to the fabrication of high resistivity zones in such devices by ion bombardment.
Ion bombardment has been utilized to produce highly resistive, typically semi-insulating, zones of semiconductor material in an otherwise low resistivity semiconductor body. These zones serve a variety of functions: device isolation, p-n junction passivation and current confinement.
In the GaAs/AlGaAs materials system a number of ionic species, including hydrogen, oxygen and neon ions, have been used to bombard the material and create high resistivity. However, hydrogen ions (protons) are by far the most commonly used in the fabrication of practical devices; for example, semiconductor laser, LEDs, photodetectors, and FETs. Within this spectrum of devices the dominant application of proton bombardment has been in the fabrication of strip geometry, gain-guided heterostructure lasers. In these lasers laterally separate, high resistivity, proton-bombarded zones constrain pumping current to flow primarily in a narrow (e.g., 5 .mu.m wide), unbombarded, low resistivity channel between the zones. For this purpose, the bombardment damage that results from the impingement of medium energy protons (i.e., 50-300 keV) on the unprotected areas yields semi-insulating material (&gt;10.sup.9 ohm-cm) to a depth of 2-3 .mu.m, J. C. Dyment et al, Journal of Applied Physics, vol. 44, p. 207 (1973).
Because of the widespread interest in similar devices fabricated in the InP/InGaAsP and InP/InGaAs materials systems, it would be desirable to have a technique to form semi-insulating zones in these materials. Although J. P. Donnelly et al, Solid State Electronics, vol. 20, p. 727 (1977), have shown that proton bombardment can be used to make highly resistive regions in p-type InP, this specific technique is not readily reproducible. The correct fluence is very critical and at high fluence, type conversion occurs, J. P. Donnelly et al, Nuclear Instruments and Methods, vol. 182/183, p. 553 (1981).
Recently bombardment of p-type InP with deuterons was reported to produce highly resistive regions (&gt;10.sup.9 ohm-cm), M. W. Focht et al, Applied Physics Letters, vol. 42, No. 11, p. 970 (1983). This technique was successfully used to make gain-guided InP lasers and to improve the device characteristics of a buried channel InP structure. Although this approach appears to bye very controllable and reproducible, there is a troublesome side effect during the bombardment procedure; namely, a deuteron-deuteron reaction that results in neutrons which are a safety hazard.